Question

我目前在使用android studio时遇到问题，因为我的checkLogIn方法似乎根本不起作用。我想知道是否有人可以指出任何明显的缺陷？

编辑：当我在主活动中调用该方法时，仍然会收到错误消息。在logcat上它显示“getSlotFromBufferLocked：unknown buffer”

//Class manages all data pertaining to the login page

public class DBHandler扩展了SQLiteOpenHelper {

//Declare constants
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "logindetails.db";
private static final String TABLE_LOGIN = "Logindetails";
private static final String COLUMN_ID = "_id";
private static final String COLUMN_LOGIN = "_logIn";
private static final String COLUMN_PASS = "_password";

//Constructor
public DBHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version){
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}

//On create method - passes through a database object
public void onCreate(SQLiteDatabase db){
    //Declares column and table names and data types
    String query = "CREATE TABLE " + TABLE_LOGIN + "(" +
            COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            COLUMN_LOGIN + " TEXT," +
            COLUMN_PASS + " TEXT" +
            ");";
    db.execSQL(query);
}

//On upgrade method
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOGIN);
    onCreate(db);
}

//Adds login details to database - Takes a login object as a parameter.
public void addLogIn(LogIns log){
    //Declare values and select columns to pass values through
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();

    values.put(COLUMN_LOGIN, log.get_logIn());
    values.put(COLUMN_PASS, log.get_password());

    //Insert values into the table
    db.insert(TABLE_LOGIN, null, values);
    db.close();
}

//reads database and gets list of logins - takes the username and password as an argument
public boolean checkLogIn(String user, String pass){
    //Declare and initialise variables
    boolean success = false;
    SQLiteDatabase db = this.getReadableDatabase();
    //select columns in a string array
    String[] columns = {COLUMN_LOGIN, COLUMN_PASS};

    //execute query
    Cursor c = db.query(TABLE_LOGIN, columns, null, null, null, null, null);

    //Temp string to store results from query
    String rName = "";
    String rPass = "";

    //loop through all rows and data
    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){
        int iName = c.getColumnIndex(COLUMN_LOGIN);
        int iPass = c.getColumnIndex(COLUMN_PASS);
        rName = c.getString(iName);
        rPass = c.getString(iPass);

        if (user.equals(rName) && pass.equals(rPass)){
            success = true;
            break;
        }
    }
    return success;

}

}

Answer 1

您的字符串比较不正确。

(rName.equals(user) && rPass.equals(pass))

这可以比较引用而不是值：

private void InitializeDctionary(int typeId, IList < Game > gameInformations, IList < UserInfo > userInformations) 
{
    if (!_scoreDictionary.ContainsKey(typeId)) 
    {
        lock(_scoreDictionaryLock) 
        {

            if (!_scoreDictionary.ContainsKey(typeId)) 
            {
                _scoreDictionary.Add(typeId, new Dictionary < int, Dictionary < string, int >> ));
            }

            foreach(var gameInformation in gameInformations) 
            {
                var orderdUsers = userInformations.Where(s => s.GameId == gameInformation.Id)
                    .OrderByDescending(s => s.Score)
                    .Select((value, index) =>
                        new { value, index //this is the user rank
                        })
                    .Select(p =>new {p.value.UserName,p.index})
                    .Select(p => new KeyValuePair < string, int > (p.UserName, p.index));

                if (!_scoreDictionary[typeId].ContainsKey(gameInformation.Id))
                    _scoreDictionary[typeId].Add(gameInformation.Id, new Dictionary < string, int > ());

                _scoreDictionary[typeId][gameInformation.Id] = orderdUsers.ToDictionary(x => x.Key, x => x.Value);
            }
        }
    }
}

这会比较实际的字符串值。

进一步阅读：

How do I compare strings in Java? What is a NullPointerException, and how do I fix it?

如果您有任何问题，请在评论中告诉我。

从数据库中读取数据？

1 个答案: